The Natural Fix?

SAVANNAS AND TROPICAL GRASSLANDS Savannas cover large areas of Africa and South America and can store significant amounts of carbon, especially in their soils. Activities such as cropping, heavy grazing and in- creased frequency or intensity of fires can reduce carbon stored in these systems.

Savannas are a major component of the Earth’s vegetation and occupy large areas in Sub-Saharan Africa and South America. The savanna biome is characterised by the co-dominance of trees and grasses, but ranges from grasslands where trees are virtually absent to more forest-like ecosystems where trees are dominant. Most of the savanna areas are natural ecosystems; however, they can also be formed by the degradation of tropi- cal forests from burning, grazing and deforestation. In Africa savanna areas support a charismatic fauna of large mammals and opportunities for eco-tourism are significant. The amount of carbon stored above ground depends on how much tree cover there is, and can range from less than 2 tonnes of carbon per ha for tropical grasslands to over 30 tonnes per hectare for woodland savannas. Root carbon stocks tend to be slightly higher, with estimates of 7–54 tonnes of carbon per ha. Soil carbon stocks are high compared to those of the vegetation

(~174 t C per ha, Grace et al. 2006). Savannas and tropical grass- lands are naturally subject to frequent fires, which are an im- portant component in the functioning of these ecosystems. Fire events in savannas can release huge amounts of carbon to the at- mosphere (estimated at 0.5–4.2 Gt C per year globally). However, the carbon lost is mostly regained during the subsequent period of plant regrowth, unless the area is converted to pasture or graz- ing land for cattle (Grace et al. 2006) and these ecosystems are considered currently to act overall as carbon sinks, taking up an estimated 0.5 Gt C per year (Scurlock and Hall 1998). HUMAN IMPACTS AND IMPLICATIONS FOR CARBON MANAGEMENT Human pressure on these ecosystems is still increasing and it is estimated that more than one percent of global savanna is lost annually to anthropogenic fires, cattle raising and agri- cultural activities.

Tundra Boreal forest Temperate forest Temperate grasslands, savannas and shrublands Desert and dry shrublands

Tropical and subtropical forests Tropical and subtropical grasslands, savannas and shrublands

Source: adapted from Olson et al ., 2001.

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